﻿using System;
using System.Collections.Generic;
using System.Linq;

namespace Silky.Core.Extensions.Collections.Generic
{
    public static class EnumerableExtensions
    {
        /// <summary>
        /// Concatenates the members of a constructed <see cref="IEnumerable{T}"/> collection of type System.String, using the specified separator between each member.
        /// This is a shortcut for string.Join(...)
        /// </summary>
        /// <param name="source">A collection that contains the strings to concatenate.</param>
        /// <param name="separator">The string to use as a separator. separator is included in the returned string only if values has more than one element.</param>
        /// <returns>A string that consists of the members of values delimited by the separator string. If values has no members, the method returns System.String.Empty.</returns>
        public static string JoinAsString(this IEnumerable<string> source, string separator)
        {
            return string.Join(separator, source);
        }

        /// <summary>
        /// Concatenates the members of a collection, using the specified separator between each member.
        /// This is a shortcut for string.Join(...)
        /// </summary>
        /// <param name="source">A collection that contains the objects to concatenate.</param>
        /// <param name="separator">The string to use as a separator. separator is included in the returned string only if values has more than one element.</param>
        /// <typeparam name="T">The type of the members of values.</typeparam>
        /// <returns>A string that consists of the members of values delimited by the separator string. If values has no members, the method returns System.String.Empty.</returns>
        public static string JoinAsString<T>(this IEnumerable<T> source, string separator)
        {
            return string.Join(separator, source);
        }

        /// <summary>
        /// Filters a <see cref="IEnumerable{T}"/> by given predicate if given condition is true.
        /// </summary>
        /// <param name="source">Enumerable to apply filtering</param>
        /// <param name="condition">A boolean value</param>
        /// <param name="predicate">Predicate to filter the enumerable</param>
        /// <returns>Filtered or not filtered enumerable based on <paramref name="condition"/></returns>
        public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> source, bool condition, Func<T, bool> predicate)
        {
            return condition
                ? source.Where(predicate)
                : source;
        }

        /// <summary>
        /// Filters a <see cref="IEnumerable{T}"/> by given predicate if given condition is true.
        /// </summary>
        /// <param name="source">Enumerable to apply filtering</param>
        /// <param name="condition">A boolean value</param>
        /// <param name="predicate">Predicate to filter the enumerable</param>
        /// <returns>Filtered or not filtered enumerable based on <paramref name="condition"/></returns>
        public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> source, bool condition,
            Func<T, int, bool> predicate)
        {
            return condition
                ? source.Where(predicate)
                : source;
        }

        public static PagedList<T> ToPagedList<T>(this IEnumerable<T> source, int pageIndex = 1,
            int pageSize = 20)
            where T : new()
        {
            if (pageIndex <= 0)
                throw new InvalidOperationException($"{nameof(pageIndex)} must be a positive integer greater than 0.");

            var totalCount = source.Count();
            var items = source.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
            var totalPages = (int)Math.Ceiling(totalCount / (double)pageSize);

            return new PagedList<T>
            {
                Items = items,
                TotalCount = totalCount,
                TotalPages = totalPages,
                HasNextPages = pageIndex < totalPages,
                HasPrevPages = pageIndex - 1 > 0
            };
        }

        public static bool IsNullOrEmpty<T>(this IEnumerable<T> source) 
        {
            return source == null || !source.Any();
        }
    }
}